Unhandled exception when clicking New button under Theme

Upgraded from v1.71 Beta 1 to Beta 2.
As soon as I opened the app, I went into Options.
In the Theme section I noticed there was nothing there.
Clicked on the New button.
Got an 'Unhandled exception' error. See attached screenshot.

The full message is below:

See the end of this message for details on invoking
just-in-time (JIT) debugging instead of this dialog box.

************** JIT Debugging **************
To enable just-in-time (JIT) debugging, the .config file for this
application or computer (machine.config) must have the
jitDebugging value set in the system.windows.forms section.
The application must also be compiled with debugging
enabled.